#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <math.h>

typedef  unsigned int UINT;
typedef  unsigned char BYTE;
typedef  unsigned long DWORD;

UINT Ue(BYTE *pBuff, UINT nLen, UINT &nStartBit)
{
    //计算0bit的个数
    UINT nZeroNum = 0;
    while (nStartBit < nLen * 8)
    {
        if (pBuff[nStartBit / 8] & (0x80 >> (nStartBit % 8))) //&:按位与，%取余
        {
            break;
        }
        nZeroNum++;
        nStartBit++;
    }
    nStartBit ++;


    //计算结果
    DWORD dwRet = 0;
    for (UINT i=0; i<nZeroNum; i++)
    {
        dwRet <<= 1;
        if (pBuff[nStartBit / 8] & (0x80 >> (nStartBit % 8)))
        {
            dwRet += 1;
        }
        nStartBit++;
    }
    return (1 << nZeroNum) - 1 + dwRet;
}


int Se(BYTE *pBuff, UINT nLen, UINT &nStartBit)
{
    int UeVal=Ue(pBuff,nLen,nStartBit);
    double k=UeVal;
    int nValue=ceil(k/2);//ceil函数：ceil函数的作用是求不小于给定实数的最小整数。ceil(2)=ceil(1.2)=cei(1.5)=2.00
    if (UeVal % 2==0)
        nValue=-nValue;
    return nValue;
}


DWORD u(UINT BitCount,BYTE * buf,UINT &nStartBit)
{
    DWORD dwRet = 0;
    for (UINT i=0; i<BitCount; i++)
    {
        dwRet <<= 1;
        if (buf[nStartBit / 8] & (0x80 >> (nStartBit % 8)))
        {
            dwRet += 1;
        }
        nStartBit++;
    }
    return dwRet;
}

/**
 * H264的NAL起始码防竞争机制
 *
 * @param buf SPS数据内容
 *
 * @无返回值
 */
void de_emulation_prevention(BYTE* buf,unsigned int* buf_size)
{
    int i=0,j=0;
    BYTE* tmp_ptr=NULL;
    unsigned int tmp_buf_size=0;
    int val=0;

    tmp_ptr=buf;
    tmp_buf_size=*buf_size;
    for(i=0;i<(tmp_buf_size-2);i++)
    {
        //check for 0x000003
        val=(tmp_ptr[i]^0x00) +(tmp_ptr[i+1]^0x00)+(tmp_ptr[i+2]^0x03);
        if(val==0)
        {
            //kick out 0x03
            for(j=i+2;j<tmp_buf_size-1;j++)
                tmp_ptr[j]=tmp_ptr[j+1];

            //and so we should devrease bufsize
            (*buf_size)--;
        }
    }
}

/**
 * 解码SPS,获取视频图像宽、高和帧率信息
 *
 * @param buf SPS数据内容
 * @param nLen SPS数据的长度
 * @param width 图像宽度
 * @param height 图像高度

 * @成功则返回true , 失败则返回false
 */
bool h264_decode_sps(BYTE * buf,unsigned int nLen,int &width,int &height,int &fps)
{
    UINT StartBit=0;
    fps=0;
    de_emulation_prevention(buf,&nLen);

    int forbidden_zero_bit=u(1,buf,StartBit);
    int nal_ref_idc=u(2,buf,StartBit);
    int nal_unit_type=u(5,buf,StartBit);
    if(nal_unit_type==7)
    {
        int profile_idc=u(8,buf,StartBit);
        int constraint_set0_flag=u(1,buf,StartBit);//(buf[1] & 0x80)>>7;
        int constraint_set1_flag=u(1,buf,StartBit);//(buf[1] & 0x40)>>6;
        int constraint_set2_flag=u(1,buf,StartBit);//(buf[1] & 0x20)>>5;
        int constraint_set3_flag=u(1,buf,StartBit);//(buf[1] & 0x10)>>4;
        int reserved_zero_4bits=u(4,buf,StartBit);
        int level_idc=u(8,buf,StartBit);

        int seq_parameter_set_id=Ue(buf,nLen,StartBit);

        if( profile_idc == 100 || profile_idc == 110 ||
            profile_idc == 122 || profile_idc == 144 )
        {
            int chroma_format_idc=Ue(buf,nLen,StartBit);
            if( chroma_format_idc == 3 )
                int residual_colour_transform_flag=u(1,buf,StartBit);
            int bit_depth_luma_minus8=Ue(buf,nLen,StartBit);
            int bit_depth_chroma_minus8=Ue(buf,nLen,StartBit);
            int qpprime_y_zero_transform_bypass_flag=u(1,buf,StartBit);
            int seq_scaling_matrix_present_flag=u(1,buf,StartBit);

            int seq_scaling_list_present_flag[8];
            if( seq_scaling_matrix_present_flag )
            {
                for( int i = 0; i < 8; i++ ) {
                    seq_scaling_list_present_flag[i]=u(1,buf,StartBit);
                }
            }
        }
        int log2_max_frame_num_minus4=Ue(buf,nLen,StartBit);
        int pic_order_cnt_type=Ue(buf,nLen,StartBit);
        if( pic_order_cnt_type == 0 )
            int log2_max_pic_order_cnt_lsb_minus4=Ue(buf,nLen,StartBit);
        else if( pic_order_cnt_type == 1 )
        {
            int delta_pic_order_always_zero_flag=u(1,buf,StartBit);
            int offset_for_non_ref_pic=Se(buf,nLen,StartBit);
            int offset_for_top_to_bottom_field=Se(buf,nLen,StartBit);
            int num_ref_frames_in_pic_order_cnt_cycle=Ue(buf,nLen,StartBit);

            int *offset_for_ref_frame=new int[num_ref_frames_in_pic_order_cnt_cycle];
            for( int i = 0; i < num_ref_frames_in_pic_order_cnt_cycle; i++ )
                offset_for_ref_frame[i]=Se(buf,nLen,StartBit);
            delete [] offset_for_ref_frame;
        }
        int num_ref_frames=Ue(buf,nLen,StartBit);
        int gaps_in_frame_num_value_allowed_flag=u(1,buf,StartBit);
        int pic_width_in_mbs_minus1=Ue(buf,nLen,StartBit);
        int pic_height_in_map_units_minus1=Ue(buf,nLen,StartBit);

        width=(pic_width_in_mbs_minus1+1)*16;
        height=(pic_height_in_map_units_minus1+1)*16;

        int frame_mbs_only_flag=u(1,buf,StartBit);
        if(!frame_mbs_only_flag)
            int mb_adaptive_frame_field_flag=u(1,buf,StartBit);

        int direct_8x8_inference_flag=u(1,buf,StartBit);
        int frame_cropping_flag=u(1,buf,StartBit);
        if(frame_cropping_flag)
        {
            int frame_crop_left_offset=Ue(buf,nLen,StartBit);
            int frame_crop_right_offset=Ue(buf,nLen,StartBit);
            int frame_crop_top_offset=Ue(buf,nLen,StartBit);
            int frame_crop_bottom_offset=Ue(buf,nLen,StartBit);
        }
        int vui_parameter_present_flag=u(1,buf,StartBit);
        if(vui_parameter_present_flag)
        {
            int aspect_ratio_info_present_flag=u(1,buf,StartBit);
            if(aspect_ratio_info_present_flag)
            {
                int aspect_ratio_idc=u(8,buf,StartBit);
                if(aspect_ratio_idc==255)
                {
                    int sar_width=u(16,buf,StartBit);
                    int sar_height=u(16,buf,StartBit);
                }
            }
            int overscan_info_present_flag=u(1,buf,StartBit);
            if(overscan_info_present_flag)
                int overscan_appropriate_flagu=u(1,buf,StartBit);
            int video_signal_type_present_flag=u(1,buf,StartBit);
            if(video_signal_type_present_flag)
            {
                int video_format=u(3,buf,StartBit);
                int video_full_range_flag=u(1,buf,StartBit);
                int colour_description_present_flag=u(1,buf,StartBit);
                if(colour_description_present_flag)
                {
                    int colour_primaries=u(8,buf,StartBit);
                    int transfer_characteristics=u(8,buf,StartBit);
                    int matrix_coefficients=u(8,buf,StartBit);
                }
            }
            int chroma_loc_info_present_flag=u(1,buf,StartBit);
            if(chroma_loc_info_present_flag)
            {
                int chroma_sample_loc_type_top_field=Ue(buf,nLen,StartBit);
                int chroma_sample_loc_type_bottom_field=Ue(buf,nLen,StartBit);
            }
            int timing_info_present_flag=u(1,buf,StartBit);

            if(timing_info_present_flag)
            {
                int num_units_in_tick=u(32,buf,StartBit);
                int time_scale=u(32,buf,StartBit);
                fps=time_scale/num_units_in_tick;
                int fixed_frame_rate_flag=u(1,buf,StartBit);
                if(fixed_frame_rate_flag)
                {
                    fps=fps/2;
                }
            }
        }
        return true;
    }
    else
        return false;
}
